Mechanically coupled alternatively usable cantilever structures for scanning a surface

ABSTRACT

The present invention concerns a cantilever arrangement for scanning a surface. This arrangement comprises a first cantilever having a first probe and a second cantilever having a second probe. Both cantilevers are mechanically coupled such that the second cantilever follows the movement of the first cantilever, i.e. the deflection of the first cantilever defines the deflection of the second cantilever.

TECHNICAL FIELD

The present invention relates to a special cantilever design which iswell suited for applications such as scanning probe microscopes (AFM,STM) or scanning probe storage systems, scanning lithography systems,combined atomic force/tunneling microscopes (AFM/STMs))and so forth. Thepresent invention also enables special modifications and improvements ofthe above systems.

BACKGROUND OF THE INVENTION

The development of scanning tunneling and atomic force microscopes hasled to various kinds of applications. Examples of these applicationsare: scanning probe storage systems, e.g. storage systems making use ofparallel local probes, scanning probe lithography systems, testequipment comprising a scanning probe or array of probes, atomicresolution, high throughput inspection systems, and scanning probesystem used for the structuring of surfaces;such a semiconductor chipsand the like.

Scanning probe microscopes and scanning probe storage systems making useof the tunneling current require a mechanism to ensure that the scanningprobe (or arrays of scanning probes) is kept in close proximity to thesample or storage medium. This can for example be achieved by means of aspecial cantilever carrying a probe, as disclosed in the U.S. Pat. No.5,036,490. Such a cantilever may be equipped with a piezoactuator, forexample, to allow adjustment of the distance between storage medium andprobe. To obtain a memory of sufficient storage capacity a scanningprobe system (AFM- and STM-based systems) would require hundreds ofcantilevers each of which being equipped with its own actuators anddriving circuitry. The manufacturing of such cantilevers with piezoactuators is complicated, expensive, and the reproducibility andapplicability as mass-storage devices is currently questionable.

Most atomic force scanning probe systems are operated in contact mode,i.e. the probe(s) is brought into direct contact with the sample orstorage medium. To obtain information of the sample or storage medium,the probe is scanned in contact over its surface. The operation incontact mode greatly affects the reliability of the probe, which usuallycomprises a sharp tip-like element, due to wear-out. The wear-out inturn leads to reduced reproducibility and increased cost because the tipor probe has to be replaced from time to time. Furthermore, the surfaceto be scanned may be damaged.

There are other scanning probe systems where the probe, sample, or bothtogether are oscillated. This usually leads to a situation where the tipof the probe frequently contacts the sample or storage medium. This modeof operation was, for example, addressed for the first time in thearticle "Atomic Force Microscope", G. Binnig and C. F. Quate, PhysicalReview Letters, Vol. 56, No. 9, pp. 930-933. In the following, this modeof operation is referred to as tapping mode.

As outlined above, most scanning probe systems (AFM- and STM-based)require means for adjustment/control of the distance between thescanning probe and surface to be scanned. Usually, actuators areemployed requiring driving circuitry and wiring. Dense packaging is thusdifficult.

Not only in case of high-end scanning probe systems, but also in case oflow-end systems, there is a demand for simplification of adjustment andcontrol of the distance between the probe on one hand and the sample orstorage medium on the other hand.

Some of the above systems are also designed for use in an ultra highvacuum (UHV). The dimensions of a UHV chamber area limited and scanningprobe systems of very small size are required.

It is a disadvantage of most currently available scanning probe systemsthat they are complex and expensive. Furthermore, the handling of suchsystems is usually difficult. Conventional scanning probe systems haveto be operated carefully in order to avoid damage of the local probe.

It is an object of the present invention to provide simpler and morerobust scanning probe systems.

It is an object of the present invention to provide a new, improvedcantilever design for use in connection with, or as part of any kind ofscanning probe systems, including low-end scanning probe systems.

It is a further object of the present invention to provide new orimproved scanning probe systems enabled by the inventive cantileverdesign.

SUMMARY OF THE INVENTION

This has been achieved by the provision of a new and inventivecantilever arrangement. This cantilever arrangement is characterized inthat there are at least two cantilevers being mechanically coupled. Eachof these two cantilevers comprises a probe which may differ in size,shape, material, robsutness, and so forth. The two cantilevers aredesigned and coupled such that the deflection of the second cantileverdepends on the deflection of the first cantilever.

Depending on the application, one of the cantilevers, e.g. a cantileverhaving a smaller probe, may be operated in AFM mode or STM mode. Eitherone of the two cantilevers or both cantilevers may comprise means foractuation, such as a piezo actuator for example. Instead of using meansfor fine actuation, the inventive cantilever arrangement may be designedsuch that attractive forces (adhesion) or external forces(electrostatic/magnetic) pull one of the cantilevers into contact mode.However, a fine actuator may be employed in addition to adjust (`finetune`) the distance between probe and surface to be scanned. In case ofone cantilever being operated in STM mode, a fine actuator is requiredto ensure that the tunneling distance between its probe and the surfaceis kept constant using a feedback mechanism.

DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to thefollowing schematic drawings (it is to be noted that these drawings arenot drawn to scale):

FIG. 1A shows a schematic bottom view of a first embodiment of thepresent invention.

FIG. 1B shows a schematic cross-section of the first embodiment.

FIG. 2A shows a schematic bottom view of a second embodiment of thepresent invention.

FIG. 2B shows a schematic cross-section of the second embodiment.

FIG. 3A shows a schematic bottom view of a third embodiment of thepresent invention.

FIG. 3B shows a schematic cross-section of the third embodiment, thesmaller probe being in contact mode.

FIG. 3C shows a schematic cross-section of the third embodiment, thesmaller probe not being in contact mode.

FIG. 4 shows a schematic bottom view of another embodiment of thepresent invention.

FIG. 5 shows a schematic bottom view of yet another embodiment of thepresent invention.

FIG. 6 shows a schematic bottom view of an embodiment according to thepresent invention where the larger cantilever carries two probes and thesmaller cantilever, being an integral part of the large one, carries oneprobe.

FIG. 7 shows a schematic bottom view of a cascaded cantileverarrangement according to the present invention.

GENERAL DESCRIPTION

Before different embodiments of the present invention are described, thebasic elements of scanning probe systems, in accordance with the presentinvention, are addressed. It is to be noted that the word `sample` whichis usually used in connection with scanning probe microscope systemsshall also cover storage media, electronic circuits, and semiconductorchips to be made or tested, surfaces to be structured or modified and soforth.

Cantilevers:

Cantilevers are well known elements which are easy to make. Existingsemiconductor fabrication processes can be employed. In essence, thetechniques of micromachining are employed to create discrete cantileversand arrays of cantilevers. When dimensioning such cantilevers, one hasto take into account specific parameters of the material used assubstrate in which the cantilevers are formed. When properly designing acantilever or a cantilever array, it can be mass-produced by batchprocessing at low cost and with high yield.

Usually, cantilevers are made by etching away portions of a siliconsubstrate. This substrate is normally (100) or (111) oriented. (100)oriented silicon could for example be wet etched using ethyl diaminepyrocatechol or KOH solutions. Wet etching techniques are generallydependent on crystallographic orientation of the substrate, e.g. (100)oriented silicon shows a very low etch rate of the (111) plane, leadingto a good etch stop along the (111) axis which generates well definedetch planes with 54.7⁰ angles from (100). An alternative approach makesuse of dry etching techniques, e.g. reactive-ion beam etching (RIE),chemically assisted ion beam etching, microwave assisted plasma etching,or inductively coupled plasma etching. Depending on process conditions,deep and anisotropic or isotropic structures can be obtained leading toexcellent dimensional control. Masks can be employed to define thestructures to be etched.

Likewise, cantilevers may be manufactured or modified using the focussedion beam milling technique. In this technique, a pre-fabricatedcantilever is enclosed in a vacuum chamber at a base pressure of about2.3×10⁻⁶ mbar, for example. From an ion source, gallium (Ga) ions areaccelerated by a high voltage (10-30 kV) and focussed on the target. Acurrent of 12-12000 pA is used to erode the material at the target spot.The efficiency of the process can be enhanced by directing a stream ofe.g. chloride molecules to a target area. Grooves, trenches, holes, andother constrictions can be comfortably produced by applying this method.The equipment for focussed ion beam milling is commercially available.

Focussed ion beam milling can also be used to modify conventionalcantilevers. It is for example possible to form a smaller cantilever, oran array of cantilevers in a conventional cantilever.

The cantilevers used can have any shape that can be made using the abovementioned techniques. The cross-sectional shape perpendicular to thelongitudinal axis of the cantilever could be rectangular, round,elliptical, or polygonal, for example.

Also suited for the fabrication of cantilevers are other semiconductingmaterials, like gallium arsenide, as reported in "dynainicMicromechanics on Silicon: Techniques and Devices", K. E. Petersen, IEEETransactions on Electronic Devices, Vol. ED25, No. 10, 1978, pp.1241-1249.

Local probes:

The word `probe` herein used is meant to cover any kind of structuresuited to interact directly or indirectly with the surface to beinvestigated, storage medium to be interacted with, or surface to bestructured or modified. It also includes AFM and STM kind of probes.Usually a tip or a ball-like element is used as probe. Differenttechniques are known to produce such probes. They can, for example, bemade by isotropic wet or dry etching in combination with the oxidationof a single crystal material, such as silicon.

The following materials are well suited for making local probes andlocal probe arrays: tungsten, tungsten alloy, platinum, molybdenum,silicon (doped or undoped), doped diamond, any refractory metal, orconductive ceramics, to name some. The combination of wet or dry etchingand liftoff plus oxidation leads to very sharp pointed cones. Thesharper the tips are, the denser information on a storage medium can bestored, leading to increased capacity of a storage device. Or, in caseof a scanning probe used to investigate a sample, the radius of the tipis directly related to the resolution of the scanning system. The probescan be coated with an appropriate metal such as gold, for example. InU.S. Pat. No. 5,204,581, it is described in detail how to make tips orarrays of tips; which can be used in connection with the presentinvention. Another example for the microfabrication of a tip isdisclosed in the article "Silicon cantilevers and tips for scanningforce microscopy", J. Brugger et al., Sensors and Actuators A, Vol. 34,1992, pp. 193-200. It is important to note that by means of batchfabrication local probes can be made in a reproducible and cheap manner.In particular large probes can be made by means of electro-plating. Toachieve this, a plating base is required to define the position wherethe probe is to be formed.

According to the present invention, there are always at least twoprobes. These probes may differ in size, shape, robustness, or materialE.g., one of the probes may be substantially smaller than the other one,or one probe may be softer than the other probe. As will be seen inconnection with the embodiments, it is advantageous to employ one probeof larger size in order to reduce damages of the surface to be scannedand ruining of the smaller probe which is usually more sensitive toforces, or to generate lower resolution images in a large scan mode. Inaddition, the larger probe may be made using a soft material.

Scan movement:

Different approaches for achieving a scan movement of the probes withrespect to the storage medium, sample, or surface can be employed. Therespective means are referred to as actuators. One can use a variety ofscanning schemes including pulsed and continuous scanning. Furthermore,the scanning speed may be varied and means to allows zoom-in can besupported.

The different cantilever movements which can be achieved with anintegrated piezoelectric actuator are described in the published PCTpatent application WO 89/07256.

Actuators:

As indicated above, each cantilever, or cantilever array may comprise anactuator so as to displace it from a relaxed position to a deflectedposition or vice versa. Scan movement is obtained by actuators designedfor lateral cantilever displacement. The distance between probe andsurface to be investigated may be controlled using actuators forvertical displacement. The displacement achieved by an actuator might bedamped to prevent damage and to allow better and more precise operation.Special means for damping may be employed which allow to provide adamping factor depending on the displacement. It is also possible to usedamping means which can be switched or controlled to allow adaptation ofthe damping behavior. This can be done by controlling the viscosity of aliquid material by altering its temperature.

Piezoceramic (piezoelectric) actuators are well known in the art andhave been employed in different kinds of scanning probe systems. Suchpiezoceramic actuators allow for displacements in the μm range. Apiezoelectric actuator for micromechanical devices is for exampledescribed in Sensors and Actuators, A21-A23 (1990), pp.226-228 by F. R.Blom et al. A voltage applied to the actuator gives rise to a deflectionof the cantilever to which said actuator is attached or of which it isan integral part.

Numerous proposals are known to exploit the piezoelectric material ofthe cantilever in order to control its deflection when approaching thesurface to the sample. Examples for these proposals are found in theEuropean patent application EP-A-0 492 915, showing different ways ofproducing cantilever probes with several piezoelectric layers and anappropriate number of electrodes to apply a voltage to the piezoelectriclayers. U.S. Pat. No. 4,906,840 discloses a similar layered cantileverstructure with a piezoelectric bimorphous layer allowing the cantileverbeam to be bent in opposite directions from its rest position. In someembodiments, the control circuitry necessary to load the piezoelectricbimorph is proposed to be integrated into the substrate from which thecantilever is etched.

Another kind of actuator is disclosed in copending FPCT patentapplication with publication No. WO96/07074. The actuator disclosedtherein is based on the well-known principle of magneticinduction/magnetomotive force. The effect of magnetic induction ischaracterized by the force that a magnetic field or the change of amagnetic field exerts upon a magnet, a current carrying conductor or anotherwise magnetized material within this field. The forces induced arecontrolled by means of reducing gear and damping means. The magneticinduction actuator is particularly well suited for realizing simple butreliable positioning of a probe with respect to a sample or vice versa.

Another example is a capacitive actuator which is activated by applyinga voltage between two electrodes (electrostatic deflection)

Instead of using an actuator driven by a current or voltage, an actuatormay be employed which can be activated by inducing heat, e.g. by meansof a light beam. The heat introduced may lead to an expansion of certainlayers or portions forming the actuator. The expansion in turn may causea deflection of a cantilever. The heat may likewise be generated by avoltage drop at a resistor formed in or at the cantilever.

Instead of using an actuator, the inventive cantilever arrangement maybe designed such that attractive forces (adhesion) pull one of thecantilevers into contact mode.

Most of the actuators need appropriate wiring and driving circuitry. Ina system where a probe is to be operated in contact mode, means have tobe provided which allow to `switch` the probe into contact mode. Thiscan either be done using an actuator for vertical displacement, or bymeans of appropriately designed cantilevers which are soft enough to beattracted by the sample to be investigated. In the latter case the dualcantilever structure, according to the present invention, is very simplebecause no actuator for bringing the probe into contact mode isrequired. However, if a suited actuator is employed it is possible toactively switch the probe into contact mode position and vice versa.

An STM-based scanning probe system demands for good control of thedistance between second cantilever and sample to be investigated. Thisdistance may be actively adjusted/controlled by means of an actuator forvertical displacement.

Coarse Actuators:

For most applications the present cantilever arrangement renders coarseactuators unnecessary. The position of one of the cantilevers depends onthe size, shape, and position of the other cantilever to which it ismechanically coupled i.e., the second cantilever follows the movement ofthe first cantilever, for instance. Nevertheless, a coarse macroscopicvertical displacement adjustment might be advantageous under certaincircumstances. Coarse displacement can be used to compensatemanufacturing tolerances and to move the present cantilever arrangementinto a park position when not being used, for example. For coarsedisplacement PZT (a piezoelectric ceramic material; Lead ZirconateTitanate) actuators or precision levers and micrometer screws can beused.

The above mentioned actuators need specific driving circuitry which caneither be integrated onto the cantilever substrate, or which can becarried out separately.

As described above, any kind of actuator can be used in connection withthe invention. For sake of simplicity details of these actuators are notshown in the Figures, or, where necessary, only illustratedschematically.

Driving circuitry:

Certain means, including driving circuitry, preamplifiers, and anappropriate wiring for reading and writing information may be provided.To make these means one can employ existing tools and processes commonto the semiconductor and solid-state industries. Depending on thespecific application, miniaturization is mandatory to obtain shortinterconnections, high speeds, and reduced power consumption. Part orall of the driving circuitry may even be integrated into the cantileverchip.

Deflection sensors:

In order to detect the deflection of an AFM scanning probe, a deflectionsensor is to be employed. The deflection of a cantilever is usuallydetected using optical or piezoresistive deflection sensors.

A piezoresistive resistor, for example, may be embedded at the fixed endof the cantilever arm. Deflection of the free end of the cantilever armproduces stress along the cantilever. That stress changes the resistor'sresistance at the base of the cantilever in proportion to thecanlilever's deflection. A resistance measuring apparatus is coupled tothe piezoresistive resistor to measure its resistance and to generate asignal corresponding to the cantilever arm's deflection. As demonstratedfor the first time in the copending patent publication No. WO97/09584filed on Sep. 1, 1995 such piezoresistive detectors can be formed in aconstriction at the fixed end of the cantilever such that it undergoeseven stronger stress.

An optical deflection sensor comprises a light source, e.g. a laserdiode, and a photodetector. The light emitted by the light source isdirected onto the cantilever and the photodiode is arranged such thatreflected light is collected by it. A deflection of the cantilever leadsto changed deflection of the light beams. This change in deflection canbe detected by said photodiode and analyzed to obtain information as toamount of displacement of the cantilever.

Both detection approaches can be applied to the present invention. It iseven conceivable to detect the movement of one of the cantilevers bymeans of a piezoresistive detector whereas an optical deflection sensoris used to detect any movement of the second cantilever.

The present invention is now described in connection with a firstembodiment. This embodiment is shown in FIGS. 1A and 1B. In FIG. 1A, abottom view of an inventive dual cantilever arrangement is shown. Thereis a first cantilever 11 having a large probe 14 close to its free end.This first cantilever 11 carries a second, smaller cantilever 13 whichin turn has a small probe 15. Such a smaller cantilever may be formed byetching away certain portions of the larger cantilever 11. In thepresent example, the second cantilever 13 is an integral part of thefirst cantilever and both cantilevers are mechanically coupled such thatthe second cantilever's deflection is defined by the deflection of thefirst cantilever 11. As illustrated in FIG. 1A, a gap 12 may be formedsuch that the second cantilever 13 is only clamped at one end. The largecantilever is formed in a substrate 10.

For better illustration, a cross-sectional view (from point A to A') ofthe two cantilevers 11 and 13 is shown in FIG. 1B. As can be seen inthis Figure, the geometry of the cantilever 11 and the probe 14 as suchdefine the distance z between the smaller probe 15 and the surface 16 tobe scanned. The smaller probe 15 now floats above the surface 16 and isprotected from being mechanically damaged because it follows themovement (deflection) of the cantilever 11. Using a suitable actuator,the smaller probe 15 may now either be brought into contact mode, e.g.enabling AFM operation, or the distance z may be varied carefully toallow STM-mode operation. The cantilever 11 may also comprise anactuator or actuators as well as deflection sensors. Neither theactuator(s) nor the deflection sensors are shown in FIGS. 1A and 1B. Theinventive dual cantilever arrangement of FIGS. 1A and 1B is suited forany kind of scanning probe systems as will be described later inconnection with examples. Such an inventive cantilever arrangement doesnot only reduce wear-out, it also allows a mode of operation where thelarger probe 14 is used for large scan excursion, e.g. in the millimeterrange. As soon as a particular scan position is reached, the smallerprobe 15 may than be used for zoom-in, i.e. for scanning a smallerportion of the surface 16 with higher resolution. In another mode, bothprobes can be operated simultaneously. The output signal of the twoprobes have to be processed in an appropriate manner to obtaininformation from the surface scanned.

Another, more detailed embodiment is illustrated in FIGS. 2A and 2B. Inthis case the cantilevers are triangular shaped. There is a firstcantilever 21 with large probe 24 carrying a second cantilever 23 with asmaller probe 25. As described above, the second cantilever 23 may beformed by structuring the first one. Likewise, the second cantilever maybe produced separately for later attachment to the first cantilever 21.In FIG. 2A, further details are shown. The second cantilever 23, forexample, carries metallization 28 for electrically heating the probe 25.In the present embodiment, there is a resistor (not shown) underneaththe probe 25 which heats the probe if a voltage is applied betweencontact pads 18 and 19. Such an arrangement may be used in athermomechanical storage system, where information may be stored byforming indents in a storage medium using the heated probe. Furthermore,the smaller cantilever 23 comprises constrictions at its clamped end inorder to reduce the stiffness. Piezoresistive sensors 29 are integratedinto these constrictions to obtain deflection sensors of highsensitivity. The piezoresistive sensors 29 are connected with thecontact pads 17 and 18. In addition to the constrictions, the cantilevermay have etch holes 27 at its fixed end. These etch holes, in additionto the constrictions, lead to a further reduction of the cantilever'sstiffness. Details of such sensors are given in the above mentionedcopending PCT patent publication WO97/09584. The cross-sectional viewgiven in FIG. 2B is essentially the same as the one in FIG. 1B. The onlydifference is that there is the metallization 28 and a piezoelectricsensor 29 shown. As in case of the first embodiment, the cantilever 23with small probe 25 can be actuated by means of an actuator or severalactuators (not shown). The large cantilever 21 may also comprise anactuator or several actuators, e.g. to bring it into a park positionwhere even the large probe 24 is removed from the sample 26. Not onlythe smaller cantilever, but also the large cantilever may comprise meansfor deflection sensing

A more sophisticated cantilever arrangement (third embodiment) isillustrated in FIGS. 3A, 3B, and 3C. In this embodiment, the cantilever33 carrying the large probe 34 is an integral part of the largercantilever carrying a small probe 35, i.e., in this embodiment thesmaller cantilever 33 carries the larger probe 34. The larger cantilever31 is mechanically connected at the end opposite to its free end to saidsmaller one such that it mainly follows the movement (deflection) of thesmaller cantilever 33. For this reason the legs 37 of the largercantilever 31 are relatively thick such that it is stiff and follows thesmaller cantilever 33. This arrangement has been further elaborated byproviding thin portions 38. Due to these thin portions 38 provided insaid larger cantilever 31, a kind of a third cantilever portion 39 isobtained. As illustrated in FIG. 3C, this cantilever portion 39 is in aposition where the small probe 35 contacts the sample surface 36 ifcantilever 33 with large probe 34 is in `park` position. The thinnedportions 38 lead to a reduced stiffness. The movement of the cantileverportion 39 can be better understood assuming a virtual axis (see FIG.3A). By provision of suitable actuators, various operation schemes forthe cantilever arrangement of FIGS. 3A-3C can be achieved. The innercantilever 33 may be switched up and down by means of an actuator at itsclamped end.

In the present case, this actuator comprises a heating element 42 withmetallizations 40 and contact pads 43 and 44. On the opposite side ofthe cantilever 33, there is a metal plate 41 having a larger thermalexpansion coefficient than the cantilever. The cantilever 33 is in the`park` position (see FIG. 3B) if no current flows through the heatingelement 42. By applying a voltage between contact pads 43 and 44, acurrent heats the heating element 42 and the fixed end of cantilever 33.The increased temperature in the cantilever leads to an expansion ofmetal plate 41 which in turn generates a bending force switching thecantilever 33 into contact mode (see FIG. 3C). In this case, the smallerprobe 35 does not contact the sample 36 anymore. Using a suitablematerial having a smaller expansion coefficient than the cantileversitis possible to place a plate on the same side of the cantilever as allother elements 28, 29, etc. A shape-memory alloy (SMA) may also be usedfor switching the cantilever.

Other modes of operation are possible if the larger cantilever comprisesactuators at its thick legs 37 so as to move the whole cantilever 31together with the cantilever portion 39. Likewise, or in addition, thecantilever portion 39 may be individually actuated employing actuatorsat the thin portions 38, or close to these thin portions. The stiffnessof the cantilever portion 39 may be chosen such that the cantileverportion 39 automatically flips into contact mode if the z-distance fallsbelow a certain minimum distance such that the attractive forces(adhesion) are stronger than the spring force of the cantilever portion39.

Further embodiments of the present invention are given in FIGS. 4 and 5.As can be seen in FIG. 4, there is a large cantilever 51 carrying threesmaller cantilevers 53. The large cantilever 51 has a large probe 54 andeach of the smaller cantilevers 53 carries a small probe 55. A similararrangement is illustrated in FIG. 5. In this Figure, the largercantilever 61, having a large probe 64, and carries three triangularshaped smaller cantilevers 63, each carrying a small probe 65. Thesesmaller cantilevers 63 are arranged in an interlocked manner. These kindof cantilever arrangements, following the basic principle of the presentinvention are particularly well suited for scanning probe storageapplications where an increased data throughput can be obtained by usingcantilever arrays for parallel operation. If one employs a cantileverarrangement as shown in FIGS. 4 and 5 in a scanning probe microscope,one scan movement is sufficient to scan three parallel lines.

Another embodiment is illustrated in FIG. 6. This embodiment ischaracterized in that it comprises a larger cantilever 71 being fixed atone end to a substrate 70. At the fixed end of cantilever 71 there is aetch hole 73 employed to modify the stiffness. Close to the etch holethere are deflection sensors 79 situated. At the free and of cantilever71 a smaller cantilever 76 is formed. As the larger cantilever 71, thissmaller cantilever 76 may comprise an etch hole 77 and deflectionsensors 78, for example. Cantilever 71 has two probes 74 at its freeends 72 and the cantilever 76 one probe 75. As illustrated, the twoprobes 74 may be of larger size than the probe 75 carried by cantilever76. There are various modes of operation conceivable and differentarrangements of sensors and actuators (other than the specificarrangement shown) possible.

An embodiment with cascaded cantilevers is shown in FIG. 7. There areseveral smaller cantilevers 83, 82, and 86 being an integral part of alarge cantilever 81. The largest cantilever 81 and second largestcantilever 83 are provided with deflection sensors 89 and 87,respectively, in the present example. The smallest cantilever 86 mayalso comprise means for sensing the deflection. The smaller thecantilevers are, the smaller the respective probes 84, 85, 88, are inthe present example, i.e., the cantilever 86 comprises the smallestprobe 88. By appropriate processing of the signals from the deflectionsensors, various information concerning the scanned surface can beobtained. One of the cantilevers may for example be employed fortracking purposes. This can be achieved by providing a special patternon the surface to be scanned. Likewise, a groove can be formed on thesurface to be investigated such that the tracking cantilever ismechanically guided along this groove. Tracking is of particularimportance if one scans a storage medium with a cascaded cantilever, asherein disclosed, or a cantilever array.

One cantilever of the present cantilever arrangement, e.g. thecantilever with the smaller probe, might be operated in a dynamic mode.In this dynamic mode, the respective cantilever is approached to thesample surface and the vibration amplitude is damped. This leads to adecreased resonant frequency which may be used to obtain informationconcerning the surface scanned. The distance between vibrating secondcantilever and surface is mainly defined by the geometry of thecantilever with the larger probe.

The present cantilever arrangement may also be operated such that one ofthe probes frequently contacts the sample to be scanned. This mode ofoperation is known as tapping mode.

The present cantilever arrangements can be used to make current scanningprobe microscopes more reliable by reducing wear out. As indicatedabove, the cantilever arrangement facilitates also new modes ofoperation. The larger probe may be used for longer and/or faster scanexcursion and operation with lower resolution. The smaller probe may beused for zooming in if a position of interest has been found, i.e., thesmaller probe may be scanned in smaller steps and only with a smallerscan excursion.

In another mode of operation, one of the probes may be operated in STMmode whereas the other probe is operated in AFM mode. Using thisapproach, one gets additional information by just scanning a sampleonce. The two signals provided by the AFM probe and the STM probe can befed through a data acquisition system as claimed in copending patentpublication No. WO96/35943 filed May 13, 1995. Due to the additionalinformation obtained by the second probe, images of higher resolutionare obtained.

The present invention is well suited for use in scanning probe storagesystems. As in case of scanning probe microscopes, the larger probe maybe employed to prevent mechanical wear out of the smaller probe.Likewise, or in addition, the smaller probe may be used for reading andwriting of bits, whereas the large probe may be used for erasing storedinformation.

What is claimed is:
 1. Cantilever arrangement for scanning a surface,said arrangement comprising a first cantilever having at least a firstprobe and a second cantilever having a second probe said firstcantilever and said second cantilever being mechanically coupledtogether such that the deflection of said second cantilever depends onthe deflection of said first cantilever, said cantilever arrangementfurther comprising actuator means for bringing the second probe from anon-operational mode into an operational mode while the first probe isin an operational mode.
 2. The cantilever arrangement of claim 1,wherein either said second cantilever is an integral part of said firstcantilever, or wherein said first cantilever is an integral part of saidsecond cantilever.
 3. The cantilever arrangement of claim 1, whereinsaid first and second probes differ in size, shape, robustness, ormaterial.
 4. The cantilever arrangement of claim 1, wherein said firstcantilever is operated in contact mode while said second cantilever isnot used, or while said second cantilever is operated incontact mode,tapping or oscillation mode where said second cantilever frequentlycontacts said surface, non-contact mode, or dynamic mode.
 5. Thecantilever arrangement of claim 4, wherein said second cantilevercomprises actuator means for switching said second cantilever into therespective mode, or for operating said second cantilever in therespective mode.
 6. The cantilever arrangement of claim 1, wherein saidsecond cantilever is designed such that attractive forces, or externallycontrollable forces pull said second cantilever into contact mode. 7.The cantilever arrangement of claim 1, wherein said second cantilevercomprises oscillator means for oscillating said second cantilever suchthat said second cantilever either frequently contacts said surface, oroscillates without contacting said surface.
 8. The cantileverarrangement of claim 1, wherein said first cantilever and/or said secondcantilever comprises a sensor for movement detection.
 9. The cantileverarrangement of claim 8, wherein said sensor for movement detection is apiezoresistive sensor, situated in a constriction at the fixed end ofthe respective cantilever whose movement is to be detected.
 10. Thecantilever arrangement of claim 1, comprising means for heating one ofsaid probes for interaction with said surface.
 11. Cantileverarrangement for scanning a surface, said arrangement comprising a firstcantilever having at least a first probe and a second cantilever havinga second probe said first and second cantilevers being mechanicallycoupled such that the deflection of said second cantilever depends onthe deflection of said first cantilever, wherein said first cantilevercomprises actuator means for switching said first cantilever intocontact mode, said second cantilever being mechanically coupled withsaid first cantilever such that said second cantilever is in non-contactmode if said first cantilever is in contact mode and vice versa.
 12. Thecantilever arrangement of claim 11, wherein one of the two cantileverscomprises a third cantilever portion thereof which can be deflectedrelative to a remaining portion of said one cantilever.
 13. Thecantilever arrangement of claim 11, wherein said actuator meanscomprises a heating element for locally increasing the temperature insaid first cantilever and means for generating a bending force if thetemperature increases.
 14. Cantilever arrangement for scanning asurface, said arrangement comprising a first cantilever having at leasta first probe and a second cantilever having a second probe said firstand second cantilevers being mechanically coupled such that thedeflection of said second cantilever depends on the deflection of saidfirst cantilever, wherein said first cantilever comprises multiplesmaller cantilevers.
 15. The cantilever arrangement of claim 14, whereinsaid first cantilever comprises cascaded smaller cantilevers. 16.Scanning probe system comprising a cantilever arrangement according toany of the preceding claims.
 17. The scanning probe system of claim 16,being used for inspection of semiconductor chips, for investigation ofsample surfaces, or for structuring surfaces.
 18. The scanning probesystem of claim 17, comprising means for scanning said semiconductorchips, sample surfaces, or surfaces to be structured with said firstprobe at lower resolution than said second probe.
 19. The scanning probesystem of claim 17, comprising means for scanning said semiconductorchips, sample surfaces, or surfaces to be structured with said secondprobe at lower resolution than said first probe.
 20. The scanning probesystem of claim 17, comprising means for switching between lowresolution and high resolution.
 21. The scanning probe system of claim16, being part of a storage system.
 22. The scanning probe system ofclaim 21, wherein said cantilever arrangement is used for reading anderasing information from a storage medium, and for writing informationonto said storage medium.